The present invention relates to an ultrasonic transducer device comprising a plurality of transducer elements arranged in rows and columns and acoustic insulation material maintained between adjacent transducer elements, for converting electrical energy into ultrasonic wave energy to be radiated into the water and vice versa. Particularly, the invention relates to the improved structure of the transducer device.
The transducer elements may be disposed on a plane in rows and columns at uniform or different space intervals in one of mutually perpendicular directions or in both directions thereof, thereby forming a planar array of the transducer elements. The transducer elements may be disposed in rows and columns along the circumference of a cylinder at uniform or different space intervals, thereby forming a cylindrical array. As the transducer elements, magnetostrictive or electrostrictive ultrasonic transducers may be used.
An ultrasonic tranducer device of this type has been proposed by the applicant and disclosed in a laid-open Japanese Patent Application No. 25080 of 1981. Referring to FIGS. 1, 2 and 3, the conventional transducer device will be explained. Numerals 1, 1 . . . are magnetostrictive transducer elements of the II-type. Thirty of the transducer elements are disposed on an imaginary circle at angular uniform intervals, thereby forming a circular row of the transducer elements. There are ten such rows from the top of the bottom of the transducer assembly. The transducer elements of each row are acoustically insulated from the ones of rows adjacent thereto by transducer liners 2, 2 . . . and 3, 3 . . . made of acoustic insulation material such as cork or urethane foam. The outer transducer liner 2 and the inner transducer liner 3, each shaped in a ring form, are disposed concentrically on an imaginary plane, as illustrated in FIG. 3. The II-type magnetostrictive transducer elements 1, 1 . . . are circularly mounted on the transducer liners 2 and 3 at uniform angular intervals in radially extending relation. The transducer elements are disposed on the transducer liners 2 and 3 in a manner that the sound sensing part of each one of the transducer elements 1 is supported by the outer transducer liner 2 and the leg parts thereof are supported by the inner transducer liner 3, as shown in FIG. 2. The sound sensing part 1A of each one of the transducer elements is stuck to the outer transducer liner 2, and the leg parts thereof are supported by the inner transducer liner 3 with their surfaces merely kept in contact with the surface of the transducer liner 3 so that their vibration energy can be activated by coils 1C in a form of electric signal. Each of permanent magnets 4 is maintained between the legs of respective one of the transducer elements 1 to provide a biasing magnetic field, and is fixed to the inner transducer liner 3. The front surfaces of the transducer elements arranged in thirty straight columns and ten circular rows with the transducer liners 2, 3 being inserted between the adjacent rows of the transducer elements, are covered by sound passing material Rho-C rubber such as urethane rubber, which is molded. Ultrasonic waves are transmitted and received into and from the water through the molded cover 5. Thus, the outer transducer liners 2 are supported by the cylindrically shaped molded cover 5. Each one of the transducer elements 1 is stuck to the outer transducer liners 2. The inner transducer liners 3 support the leg parts 1B of the transducer elements 1. Each one of the permanent magnets 4 maintained between the leg parts the each transducer element 1 is stuck to the inner transducer liner 3. Hence, the inner transducer liners 3 are concentrically disposed with respect to the outer transducer liners 2. The transducer elements in rows and columns and the transducer liners maintained between adjacent rows of the transducer elements are arranged in a cylindrical form. The cylindrical transducer assembly is closed by an upper end head 6 and a lower end head 7 water-tightly by means of support shafts 8 and cap screws 8.
Thus, the conventional transducer device has been constructed in a manner that the transducer elements arranged in ten circular rows and the transducer liners 2, 3 maintained on and beneath each row of the transducer elements are pressed by the upper and lower end heads 6, 7 to be held. The transducer liners 2, 3 must be made of hard material so that the transducer liners are not deformed due to the pressure imposed by the end heads 6, 7. Cork or urethane foam have been employed as the hard material. These materials perform the acoustic shielding between the transducer elements of the two adjacent rows, since air is contained in small holes extensively formed therein. When pressing forces are applied to the material, the small holes shrink by small amounts, thereby reducing the whole material in size by a small amount. In order to cope with this problem, the transducser liners 2 and 3 have been manufactured a little larger than desired. A desired thickness of each one of the transducer liners has been obtained by the pressing force applied thereto when the transducer device is assembled as illustrated in FIG. 1, thereby shrinking the transducer liners.
However, it is impossible to manufacture the transducer liners 2, 3 in such a way that the height of each one of the transducer liners is exactly the same as that of the others. The thickness of the transducer liners manufactured varies from one to another. Further, the shrinking degree of the liners differs depending on the number and size of the small holes therein containing air even if the same pressing force is applied thereto. Accordingly, when the transducer liners 2, 3 and the transducer elements 1 stacked are pressed from the upper and lower directions to be held, the shrinking degree of the transducer liners 2, 3 differs from one to another, so that the space intervals between the vertically adjacent transducer elements differ from one to another by small amounts. Such unequal space intervals between the vertically adjacent transducer elements considerably affect the performance of the transducer device. With the transducer device, the ultrasonic waves radiated from a plurality of the transducer elements or the echo signals caught thereby are combined together in phase. It is important to dispose the transducer elements at a predetermined interval between the adjacent rows of the transducer elements. If the intervals between the vertically adjacent transducer elements are different from the predetermined one, a directional pattern can not be formed in a specific direction by combining in phase the ultrasonic waves transmitted from the transducer elements or the echo signals caught thereby, or transmission or reception sensitivities, i.e., side lobes in undesired directions, increase, thus considerably deteriorating the performance of the transducer device.
Further, the pressing forces produced by the upper and lower end heads 6,7 directly act on the transducer elements 1, so that an increase of the pressing forces applies a load to the vibrational operation of the transducer elements 1. Therefore, the pressing forces produced by the heads 6, 7 must be set so that the vibrational operation of the transducer elements 1 is not affected.
The transducer assembly shown in FIG. 1 is extremely weak against a force acting on the molded cover 5 from the outside thereof. In other words, the transducer elements 1 and the stacked transducer liners 2, 3 are likely to be deformed or displaced, when forces from the outside act thereon through the molded cover 5. Accordingly, the whole transducer device shown in FIG. 1 must be housed in a dome, thus making the side of the whole device larger. The transmission loss of the ultrasonic waves becomes greater, since they are transmitted or received through the dome.
Accordingly, an object of the invention is to provide a transducer device comprising a plurality of transducer elements arranged in rows and columns, which can be easily assembled.
Another object of this invention is to provide a transducer device in which a plurality of transducer elements are precisely disposed at predetermined space intervals, so that a directional radiation or reception pattern is formed in a specific direction and the amplitude of side lobes is reduced.
One more object of this invention is to provide a transducer device which is strong enough to stand external forces acting thereon and hence can be directly exposed to the water.